Air Capital Rivet Set Kit — 5-Pc., Model# 10018 | Air Punch Rivet Tools| Northern Tool + EquipmentNorthern Industrial Swivel Connector With Air Regulator — 1/4in. Dia. | Air Couplers| Northern Tool + EquipmentNorthern Industrial Air Hammer Kit — 6-Pc. Set | Air Hammers| Northern Tool + EquipmentRJRCOOLTOOLS
Find the closest fitting rivet set and either manually or with the air hammer swag the screw slots back into shape . If using the air tool you must use the regulator and check its setting often on a block of wood .If you use anything more than just barely hammering you will destroy the casting under the screw . I can't emphasize this enough . The tool is a great advantage but comes with a significant risk . You have been warned . 3/8 In. Drive Impact Driver - Socket Drivers | MSCDirect.com
You will notice that other than the jis bits above the tools all come from the lowest price search . This one tool (the impact driver) will be in your possession till the day you die . Do not scrimp , save , shave , low ball this tool . Mac , Proto , Snap-On , Matco or a clone of their patterns . Here if it looks like crap, it is . Again , you have been warmed .
Drive the bit into the slots to reform them and then insert the hand impact into the bit/socket . With some small amount of practice you will be able to determine the correct weight and material of hammer . i do not suggest a dead blow or shot filled hammer . The default hammer is brass followed by "mild" untempered steel and then lead . I at this point the screw is still resisting your best efforts to remove it it's time for a beer and serious contemplation before you come back with heat , penetrating oil , and possibly drilling the head off .
Ive only been doing this since last week so I may be in error , YMMV.